Tension indicating device



May 9, 1964 J. D. CUMMING 3, 33, 68

TENSION INDICATING DEVICE 2 Sheets-Sheet 1 Filed March 21, 1961 INVENTORJAMES D. CUMM ING A'ITOR NEYS J. D. CUMMING TENSION INDICATING DEVICEMay 19, 1964 2 Sheets-Sheet 2 Filed March 21, 1961 365 FIG. 4

INVENTOR JAMES o. CUMMING M14 4 7234 ATTORNEYS United States Patent3,133,463 TENSIGN HNDICATENG DEVEE James D. Cumming, Have-sleek,@ntarlo, anada Filed Mar. II, 19 61, Ser. No. 9?,235 1 Claim. '(Cl.iii-62) This invention relates to tension indicating devices and, inparticular, to a tension indicating device which, when used inassociation with a bolt and nut assembly, is capable of giving a visualindication of the tension in the bolt caused by tightening the nut onthe bolt.

The invention has particular application for use in association withbolt and nut assemblies of the type known as rock bolts which aredevices used in mining and other excavating work to secure the rockwalls of such excavations against partial or total collapse.

It is an object of the present invention to provide a device of thisnature which is economical to manufacture, simple to use and install,which will give a readily obtainable indication of the tension in thebolt by visual means and which does not require special skills or toolseither .to apply or to use.

The invention will be illustrated by way of example in the followingdescription and in the accompanying drawings in which like referencenumerals denote like parts in the various views and in which:

FIGURE 1 is a perspective view of a rm'ne tunnel to which rock boltsincluding the tension indicating devices of the present invention areapplied;

FIGURE 2 is a detailed cross-sectional view through a portion of FIGURE1 showing one of the rock bolts with a tension indicating device inposition;

FIGURE 3 is a still further enlarged view, in perspective, of a portionof a rock bolt and a tension indicating device in exploded position, and

FIGURE 4 is a side elevation view of a tension indicating device in itsoperative state.

Referring now to the drawings in detail and, in particular, to FIGURE 1,it will be observed that there has been provided an excavation or tunnelof the type commonly employed in the mining art. The tunnel Ill has beendriven through rock which, in the example illustrated, may be seen tocomprise a plurality of adjacent layers or strata, several of which areindicated by reference characters 11. In FIGURE 1 it will be seen that aplurality of rock bolts, each bearing a reference numeral 12 have beeninstalled in the roof of the tunnel Ill for the purpose of bindingadjacent strata Ii. together to prevent the partial or complete collapseof the tunnel roof. Each of the rock bolts 12 may be seen to be fittedwith a tension indicating device, generally bearing reference character13.

Turning now to FIGURE 2, it may be seen that a rock bolt 12 is providedwith an expandable head 15 which, when the rock bolt 12 has beeninserted in a suitably provided drilling 16 formed in the rock mass,passing through at least one interface between adjacent strata Il, maybe expanded to grip the walls of the drilling I6 so as to secure thebolt in the position shown in FIGURES 1 and 2.

Before proceeding with a detailed description of the tension indicatingdevice 13 which is illustrated in somewhat greater detail in FIGURES 7.,3 and 4, it is convenient to point out that since the function of therock bolts is to bind adjacent strata 11 together at their interface, soas to prevent the partial or complete collapse of the walls of thetunnel or excavation, it is necessary that this binding be achieved byimparting a tension in the bolt 12 so as to hold the adjacent stratainto frictional engagement with one another. It is clear that a certaindegree of tension is necessary in order to adequately would then nolonger serve its intended purpose.

.lhldlidhd achieve this object. Similarly, of course, an excessivetension in the bolts 12 may cause the bolts to break or may cause themto elongate beyond the elastic limits of the material from which theyare made. Either of these conditions is, of course, undesirable sincethe device Similarly, once the bolt has been installed and a propertension imparted to it, it is necessary that this tension be maintainedsince if, for any reason, this tension would be relaxed or dissipated,the bolt would, under these conditions, also fail to achieve itsintended purpose.

The degree of tension which is required will vary from one installationto another and will depend upon many factors such as the inherentstability of the rock within which the bolt is installed, the diameterof the bolt, the tensile strength of the material from which it is madeand many other factors, none of which are of any real significance tothe present invention. The present invention is, however, concerned withproviding means whereby a workman may readily determine when the correcttension has been imparted to the bolt 12 at the time of installation andwhich will enable him readily to determine, upon subsequently checkingthe installation, Whether the tension has been maintained, dissipated orincreased for any one of a number of reasons.

Turning now to FIGURE 3 of the drawings, the rock bolt 12 may be seenextending from the drilling 16 in the rock face 14. The free end 12aextends downwardly from the rock face 14 and is provided, adjacent theend 12a, with a suitably screw-threaded portion 18.

When studying FIGURE 3 it will be apparent that the screw-threadedportion 18 does not, in the illustrated embodiment, extend for asufficient distance along the bolt 12 for the nut 17 to be tightened soas to bring the com ponent parts into contact with one another. It musttherefore be assumed that either the rock bolt 12 may and will beinserted further into the drilling id or that the threads, although notso illustrated, will extend along the bolt 12 for a distance suflicientfor the device to be operative.

The tension indicating device includes first of all a washer, indicatedgenerally by reference character 19, which consists of an annularperipheral flange 2% surrounding, and integrally formed with the base 21of a central domed portion 22, which is provided with an aperture 23 forthe passage of the bolt 12. The aperture 23 may be in the form of a slotlying along a line of longitude of the domed portion. The slot extendsfrom a first end 23a which lies adjacent the flange 20 to a second end23b which is so located that the bolt 12 may pass through the aperture23 with the axis of the bolt concentric with the flange 20 and with theflange 20 normal to the axis of the bolt.

The washer 19 is formed of a material such as'steel which is thickenough to enable it to withstand the cornpressive force necessary toimpart the desired tension to the bolt 12 without experiencing anynoticeable deformation. The portion 22 is domed, since, as is wellknown, a domed member can support a greater compressive force than aflat surface of equivalent thick ess and for all practical purposes, thewasher 19 may be considered to be incompressible due to a force exertedalong the axis of the bolt 12 when the bolt 12 is in a position suchthat it passes through the aperture 23.

The tension indicating device comprises, as an essential feature, theU-shaped member 24 which is provided with a central aperture 2 5 throughwhich the bolt 12 may pass. The area 26 surrounding the central aperture25 constitutes a bearing surface against which the nut 17 may bear.Preferably, a hardened planar washer 27 lies between the nut 17 and thebearing surface 26 so that as the nut 17 is tightened down, it will turnagainst the washer 27 and will not gall or dig into the material of theU- shaped member 24.

The U-shaped member 24 is formed with two legs 28 and 29, each of whichis provided, adjacent its end, with a second bearing surface, bearingsurface 30 being provided on leg 28 and, bearing surface 31 beingprovided on leg 29, which second bearing surfaces are adapted to lie onthe surface of the domed portion of the washer 19, preferably throughthe medium of a sheet metal protective member 32 which, for the moment,will be ignored.

The distance between the bearing surfaces 30 and 31 will be seen to beless than the maximum diameter of the domed portion 22 of the washer 19so that these bearing surfaces will lie upon the domed surface of thecentral portion 22 of the washer 19 at positions such as thoseillustrated in FIGURES 2 and 4.

Returning now to FIGURE 2, it will be seen that as the nut 17 istightened on the threaded portion 18 of the free end 12a of the rockbolt 12, the domed portion 22 of the washer 19 will be forced betweenthe legs 28 and 29 of the U-shaped member 24 and will urge the legs 28and 29 apart. The U-shaped member 24 is made of a resilient materialsuch as steel and is of a thickness such that the force required tospread the legs apart is commensurate with the tension which it isdesired to impart to the bolt 12.

In FIGURE 3, one embodiment of the sheet metal protective member 32 maybe seen to comprise a central portion 33 which is of a curvaturecomplementary to the curvature of the domed portion 22 of the washer 19so that, as seen in FIGURE 4, it will lie adjacent the surface 22 of thewasher 19. The ends of the protective member 32 are provided withoutwardly extending tabs 34 the side edges of which may conveniently beprovided with flanges 35 which, with the tabs 34 define channels withinwhich the extremities 36 of the legs 28 and 29 of the U-shaped membermay rest. The protective member 32 performs two important functions.First, it eliminates the wear or abrasion of the domed portion 22 of thewasher 19 by the action of the U-shaped member as the bearing surfaces36 and 31 move thereover during application, removal, and adjustment ofthe device. Second, it carries the tabs 34 and flanges 35 whichconstitute reference points against which the position of theextremities of the legs of the U-shaped member may be measured.

In FIGURE 4, the tension indicating device 13 is shown in its operativestate. The bolt 12 has been installed within the rock strata 11 byinserting it in a suitable drilling and the buried end of the bolt 12 isengaged within the aperture by means of an expanding head such as thatshown, for example, at in FIGURE 2. Over the free end 12a of the bolt 12there has been applied, first of all the washer 19, secondly theprotective member 32, thirdly the U-shaped member 24, fourthly theplanar Washer 27 and finally the nut 17. As the nut 17 is tightened downon the bolt 12 it bears, through the medium of the washer 27, on thearea 26 surrounding the central aper ture in the U-shaped member 24through which the bolt 12 passes. As the nut bears on this area of theU-shaped member 24 the bearing areas 30 and 31 bear against the domedsurface 22 of the Washer 19 through the medium of the sheet metalprotective member 32. In FIGURE 4 only bearing area 30 of leg 28 isillustrated and it may be seen to contact the sheet metal protectivemember 32 with the extremity 36 of the leg 28 lying within the channelformed by flanges 35 and the tabs 34 on the protective member 32.

Since the sheet metal protective member 32 conforms to the curvature ofthe domed portion 22 of the washer 19, its configuration and position isnot affected by the tension in the bolt 12 and its position issubstantially fixed relative to the washer 19. Tightening of the nut 17,however, forces the domed portion 22 between the legs 28 and 29 of theU-shaped member 24 and forces them apart, the greater the tension, thegreater the distance through which they are forced apart and the lesserthe tension, the smaller the distance through which they are forcedapart. Thus, the distance between the bearing surfaces 30 and 31 is afunction of the tension in the bolt 12 and this distance can readily bemeasured by visually comparing the position of the extremity 36 of thelegs 28 and 29 relative to the fixed position of the extremities of theflanges 35 carried by the sheet metal protective member 32.

In FIGURE 4 the extremity 36 of leg 28 of the U-shaped member 24 isshown in full lines to be flush with the extremities of the flanges 35carried by the protective member 32. Conveniently, this position mayrepresent a tension in the bolt 12 which is the optimum for theparticular location within which the bolt is installed and the functionwhich it is to perform. Accordingly, when the bolt is being installed,the workman tightens the nut 17 until the extremity 36 of the legs 28and 29 lie flush with the outer edges of the flanges 35 carried by theprotective member 32.

Subsequently, upon checking these installations at a later time todetermine whether the bolts are still at the correct tension, he needmerely glance at the tension indicating devices and if the extremity 36is still flush with the extremity of the flanges 35, then he is able toconclude that the tension is still being maintained at the desiredlevel. If, however, the tension has been relaxed, the U-shaped members24 will have, due to their inherent resilience, climbed up on thesurface of the domed portion 22 of the washer 19 and the extremity 36 ofthe legs 28 and 29 may then lie, for example, at the position indicatedby the dotted line 36a in FIGURE 4.

Alternatively, the tension may have increased during the elapsed timebetween installation and subsequent checking, due to one or more ofseveral reasons such as, for example, a shifting in the rock strata. Ifthe tension has increased, then the dome 22 will have been forcedfurther into the space between the bearing surfaces 30 and 31 in theU-shaped member 24 and the extremities 36 of the legs of the U-shapedmembers might, for example, lie at positions such as that indicated bythe dotted line 36b in FIGURE 4.

From the foregoing description it will be readily apparent that asimple, economical and efficient tension indicating device has beenprovided which may be applied and used without special skills andwithout special tools. The tension in the bolt may be determined withinthe limits of accuracy necessary in practice, by a simple, visualinspection which will readily disclose whether or not the extremities ofthe legs of the U-shaped members are in the desired position relative tothe tabs and flanges carried by the protective sheet metal strip 32.

In addition to achieving the objects set forth earlier in thisspecification, the invention possesses certain advantages which are ofimportance. First of all, the bolts 12 are slighlty elongated by thetension which is normally imparted to them. If the rock face 14 (seeFIGURE 4) were to be crushed under the tension imparted to the bolt 12,only a slight such crushing might be sufficient to entirely dissipatethe tension in the bolt 12 if the only resilience in the entirestructure which achieved the tension were that derived from theelongation of the bolt 12. The tension is also maintained, however, bythe resilient deformation of the U-shaped member 24 which may be of agreater magnitude when measured in a direction along the axis of thebolt 12 than is the resilient elongation of the bolt itself.Accordingly, before the tension in the bolt 12 will be completelydissipated by the movement of the washer 22 towards the rock face in thedirection of the applied tension, the rock face 14 must be crushed to amuch greater extent when the present invention is used than would be thecase if no such U-shaped member 24 were employed. Accordingly,

slight crushing or spelling of the rock, although undesirable even withthe present invention, does not produce a complete dissipation of thetension as has been found to be the case in certain devices of the priorart.

Some devices of the prior ant also enabled a reading of the tension inbolt 12 to be obtained, but only by the use of special tools whichmeasured certain deformations of material used. Such tools were notaltogether convenient to use, subject to damage in the rather roughconditions of a mine and were, accordingly, less than satisfactory. Anexample of this: latter form of prior art device may be seen in BelgianPatent No. 527,435 issued on April 15, 1954 and assigned to WingfootCorporation of Akron, Ohio, United States of America. The presentinvention does not require any special tools either for installation orto obtain a reading sufliciently accurate for the intended purpose andthe task of periodically checking the rock bolts to determine whetherthe desired tension is being maintained is very much simplified andaccelerated.

Although a preferred embodiment of the invention has been described indetail by way of illustnation, it is to be understood that modificationsof the structure, shape, arrangement and configuration of the componentsillustrated, is contemplated Within the spirit of the invention and thescope of the appended claim.

What I claim as my invention is:

Structure for use in association with a bolt and nut assembly toindicate the tension in the bolt as a result of the tightening of thenut on the bolt; comprising a washer consisting of an annular peripheralflange surrounding and integrally formed with a domed central 6 domedportion of the washer and provided with an aperture through which thebolt may pass, a resilient, generally U-shaped member having a centralaperture through which the bolt may pass, the area. surrounding theaper-.

ture consisting of a first bearing surface upon which the nut, throughthe medium of a hardened planar was r may bear, the legs of the U-shapedmember each having a second bearing surface adjacent its end adapted tobear portion having an aperture through which the bolt may pass with thedomed portion extending towards the nut, a sheet metal protective memberlying on the central on the domed portion of the Washer through themedium of the sheet metal protective member, the distance between thesecond bearing surfaces of the legs of the U-shaped member in itsrelaxed state, being less than the maximum diameter of the domed portionof the was-her, the tightening of the nut on the bolt forcing theU-shaped member against the Washer and urging the legs of the U-shapedmember to spread apart as the domed portion of the washer is forcedbetween them, the sheet metal protective member having an edge lyingadjacent each leg of the Uashaped member, the position of the edgesbeing substantially fixed relative to the domed portion and whichconstitutes a reference point from which to determine the distancebetween the extremities of the legs of the U- shaped member, saiddistance, due to the resilience of the U-shaped member, being a functionof the tension in the bolt.

References Cited in the file of this patent UNITED STATES PATENTS1,774,695 Baynes Sept. 2, 1930 2,850,937 Ralston Sept. 9, 1958 FOREIGNPATENTS 1,005,474 Germany Apr. 4, 1957 1,085,480 Germany July 21, 1960

